This invention relates to systems for supplying unmodulated video signals to television receivers. This invention also relates to systems for supplying unmodulated video and audio signals to television receivers.
There are a number of circumstances in which it may be desired to supply what could be referred to as "locally generated" video signals to a television receiver, "locally generated" signals being signals other than cable or "on-air" signals. For example, so-called TV games have become popular. The game is a locally generated video (and, often audio) signal that is supplied to a television receiver. The "locally generated" video signal also may be a serial data output signal of a computer, this being supplied to a monitor that becomes a data display unit for the computer.
In the past "locally generated" signals have been modulated and fed to the cable or antenna input of the receiver or monitor. This has disadvantages compared with a system using unmodulated signals. Firstly, resolution is poorer because limitations are imposed by the R.F. and I.F. bandwidth that is available. Secondly, the former system is more expensive than the latter because of the requirement for a modulator. Thirdly, the modulator must be designed to meet D.O.T. or F.C.C. radiation standards so that the local generator will not radiate signals that will cause interference with other equipment. Fourthly, a relatively expensive switching arrangement capable of providing about 60 db attenuation must be employed in order to prevent (a) radiation of the "locally generated" signal via the receiver antenna system and (b) interference by the "locally generated" signal with broadcast reception when the receiver mode is selected.
In accordance with this invention there is provided a system for supplying unmodulated video signals to television receivers which overcomes a number of the disadvantages of the systems referred to in the preceding paragraph.